Herm Sprenger Stainless Steel Prong Training Collar with Swivel 23" - Large 3.2mm

I bought this for our lab and if definitely works. If you buy one, buy a larger size than you really need. The size listed is max length not usual usable length. For example, if you measure the dog's neck and it's close to 23", there wont be enough play in the collar to get it over the dog's head without a real struggle (and I worry about a move that might have a prong scratch the face or eye). As shown in the photo, there is no clip so it has to go over the head.

This one of the best collars I've come across for training. Works great on my Giant Schnauzer.